There are known single solution metal surface treatment agents which comprise an organic solvent, a chromating agent or phosphoric acid and a chromating agent, a solubilizer and a stablizer and/or a reaction promotor and are able to effect degreasing and surface treatment simultaneously.
These agents comprise an organic solvent as a degreaser in which a surface treatment agent is solubilized by means of a solubilizer such as an alcohol andor a surfactant and contain other additives. As the organic solvent, chlorinated hydrocarbon, fluorochlorinated hydrocarbon, alcohols etc. are used.
Japanese Patent Publication No. 3363/67 (Du Pont), Japanese Patent Publication No. 5288/65 (Du Pont), Japanese Laid-Open Patent Publication No. 62970/81 (Tokuyama Soda), etc. disclose those treatment agents containing chlorinated hydrocarbon solvent and chromating agent; and Japanese Laid-Open Patent Publication No. 97476/80 (Nippon Paint), Japanese Laid-Open Patent Publication No. 112479/80 Nippon Paint) and Japanese Laid-Open Patent Publication No. 139679/81 (Nippon Paint) disclose compositions containing phosphoric acid and chromic acid.
These known treatment agents using chlorinated hydrocarbon solvents are, however, liable to decompose, which causes the treating bath to become unstable, the corrosion resistance of the treated articles to be insufficient, and the equipment to be corroded, etc. Therefore, when these solvents are used, several kinds of stabilizers are usually added in order to prevent decomposition thereof. However, these stabilizers react with chromic acid and impair the effect thereof, and this results in decomposition and degradation of the treating solution causing corrosion of the equipment and degraded corrosion resistance of the resulting treated articles. Under the circumstances, chromating treatment compositions using chlorinated hydrocarbon solvent are not in practical use today.
The compositions disclosed in the above mentioned Japanese laid-open patent publications of Nippon Paint contain chlorofluorocarbon solvents. However, the compositions disclosed there are phosphate treatment solutions for surface preparation to which chromic acid is added. They contain only limited amounts of chromic acid, which is nothing but an auxiliary agent for phosphate treatment in these compositions.
In order to eliminate the above-mentioned defects of the above described non-aqueous chromate treatment agents, we conducted an intensive study, and, by incorporating an organic carboxylic acid in a chlorofluorocarbon solvent, we have created a very stable substantially nonaqueous chromating treatment liquid composition, which gives chromate film having very good corrosion resistance with high coating weight.
This invention relates to a metal surface treating liquid composition comprising chlorofluorocarbon, chromic acid anhydride, a solubilizer and an organic carboxylic acid.